Re: [PATCH 2/2 v6] of: add generic videomode description

From: Steffen Trumtrar <s.trumtrar@pengutronix.de>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: devicetree-discuss@lists.ozlabs.org,
	Rob Herring <robherring2@gmail.com>,
	linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-media@vger.kernel.org,
	Tomi Valkeinen <tomi.valkeinen@ti.com>
Subject: Re: [PATCH 2/2 v6] of: add generic videomode description
Date: Mon, 8 Oct 2012 14:48:01 +0200	[thread overview]
Message-ID: <20121008124801.GD20800@pengutronix.de> (raw)
In-Reply-To: <12272414.930KpWciBg@avalon>

On Mon, Oct 08, 2012 at 02:13:50PM +0200, Laurent Pinchart wrote:
> Hi Steffen,
> 
> Thanks for the patch.
> 
> On Thursday 04 October 2012 19:59:20 Steffen Trumtrar wrote:
> > Get videomode from devicetree in a format appropriate for the
> > backend. drm_display_mode and fb_videomode are supported atm.
> > Uses the display signal timings from of_display_timings
> > 
> > Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
> > ---
> >  drivers/of/Kconfig           |    5 +
> >  drivers/of/Makefile          |    1 +
> >  drivers/of/of_videomode.c    |  212 +++++++++++++++++++++++++++++++++++++++
> >  include/linux/of_videomode.h |   41 ++++++++
> >  4 files changed, 259 insertions(+)
> >  create mode 100644 drivers/of/of_videomode.c
> >  create mode 100644 include/linux/of_videomode.h
> > 
> > diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> > index 646deb0..74282e2 100644
> > --- a/drivers/of/Kconfig
> > +++ b/drivers/of/Kconfig
> > @@ -88,4 +88,9 @@ config OF_DISPLAY_TIMINGS
> >  	help
> >  	  helper to parse display timings from the devicetree
> > 
> > +config OF_VIDEOMODE
> > +	def_bool y
> > +	help
> > +	  helper to get videomodes from the devicetree
> > +
> >  endmenu # OF
> > diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> > index c8e9603..09d556f 100644
> > --- a/drivers/of/Makefile
> > +++ b/drivers/of/Makefile
> > @@ -12,3 +12,4 @@ obj-$(CONFIG_OF_PCI)	+= of_pci.o
> >  obj-$(CONFIG_OF_PCI_IRQ)  += of_pci_irq.o
> >  obj-$(CONFIG_OF_MTD)	+= of_mtd.o
> >  obj-$(CONFIG_OF_DISPLAY_TIMINGS) += of_display_timings.o
> > +obj-$(CONFIG_OF_VIDEOMODE) += of_videomode.o
> > diff --git a/drivers/of/of_videomode.c b/drivers/of/of_videomode.c
> > new file mode 100644
> > index 0000000..76ac16e
> > --- /dev/null
> > +++ b/drivers/of/of_videomode.c
> > @@ -0,0 +1,212 @@
> > +/*
> > + * generic videomode helper
> > + *
> > + * Copyright (c) 2012 Steffen Trumtrar <s.trumtrar@pengutronix.de>,
> > Pengutronix
> > + *
> > + * This file is released under the GPLv2
> > + */
> > +#include <linux/of.h>
> > +#include <linux/fb.h>
> > +#include <linux/slab.h>
> > +#include <drm/drm_mode.h>
> > +#include <linux/of_display_timings.h>
> > +#include <linux/of_videomode.h>
> > +
> > +void dump_fb_videomode(struct fb_videomode *m)
> > +{
> > +        pr_debug("fb_videomode = %d %d %d %d %d %d %d %d %d %d %d %d %d\n",
> 
> That's going to be pretty difficult to read :-) Would it make sense to group 
> several attributes logically (for instance using %ux%u for m->xres, m->yres) ?
> 

No problem. That can be changed.

> > +                m->refresh, m->xres, m->yres, m->pixclock, m->left_margin,
> > +                m->right_margin, m->upper_margin, m->lower_margin, +      
> >          m->hsync_len, m->vsync_len, m->sync, m->vmode, m->flag);
> > +}
> 
> Shouldn't this (and the other non exported functions below) be static ?
> 

Yes.

> > +void dump_drm_displaymode(struct drm_display_mode *m)
> > +{
> > +        pr_debug("drm_displaymode = %d %d %d %d %d %d %d %d %d\n",
> > +                m->hdisplay, m->hsync_start, m->hsync_end, m->htotal,
> > +                m->vdisplay, m->vsync_start, m->vsync_end, m->vtotal,
> > +                m->clock);
> > +}
> > +
> > +int videomode_from_timing(struct display_timings *disp, struct videomode
> > *vm,
> > +			int index)
> > +{
> > +	struct signal_timing *st = NULL;
> > +
> > +	if (!vm)
> > +		return -EINVAL;
> > +
> 
> What about making vm a mandatory argument ? It looks to me like a caller bug 
> if vm is NULL.
> 

The caller must provide the struct videomode, yes. Wouldn't the kernel hang itself
with a NULL pointer exception, if I just work with it ?

> > +	st = display_timings_get(disp, index);
> > +
> 
> You can remove the blank line.
> 
> > +	if (!st) {
> > +		pr_err("%s: no signal timings found\n", __func__);
> > +		return -EINVAL;
> > +	}
> > +
> > +	vm->pixelclock = signal_timing_get_value(&st->pixelclock, 0);
> > +	vm->hactive = signal_timing_get_value(&st->hactive, 0);
> > +	vm->hfront_porch = signal_timing_get_value(&st->hfront_porch, 0);
> > +	vm->hback_porch = signal_timing_get_value(&st->hback_porch, 0);
> > +	vm->hsync_len = signal_timing_get_value(&st->hsync_len, 0);
> > +
> > +	vm->vactive = signal_timing_get_value(&st->vactive, 0);
> > +	vm->vfront_porch = signal_timing_get_value(&st->vfront_porch, 0);
> > +	vm->vback_porch = signal_timing_get_value(&st->vback_porch, 0);
> > +	vm->vsync_len = signal_timing_get_value(&st->vsync_len, 0);
> > +
> > +	vm->vah = st->vsync_pol_active_high;
> > +	vm->hah = st->hsync_pol_active_high;
> > +	vm->interlaced = st->interlaced;
> > +	vm->doublescan = st->doublescan;
> > +
> > +	return 0;
> > +}
> > +
> > +int of_get_videomode(struct device_node *np, struct videomode *vm, int
> > index)
> 
> I wonder how to avoid abuse of this functions. It's a useful helper for 
> drivers that need to get a video mode once only, but would result in lower 
> performances if a driver calls it for every mode. Drivers must call 
> of_get_display_timing_list instead in that case and case the display timings. 
> I'm wondering whether we should really expose of_get_videomode.
> 

The intent was to let the driver decide. That way all the other overhead may
be skipped.

> > +{
> > +	struct display_timings *disp;
> > +	int ret = 0;
> 
> No need to assign ret to 0 here.
> 

Ah, yes. Unneeded in this case.

> > +
> > +	disp = of_get_display_timing_list(np);
> > +
> 
> You can remove the blank line.
> 
> > +	if (!disp) {
> > +		pr_err("%s: no timings specified\n", __func__);
> > +		return -EINVAL;
> > +	}
> > +
> > +	if (index == OF_DEFAULT_TIMING)
> > +		index = disp->default_timing;
> > +
> > +	ret = videomode_from_timing(disp, vm, index);
> > +
> 
> No need for a blank line.
> 
> > +	if (ret)
> > +		return ret;
> > +
> > +	display_timings_release(disp);
> > +
> > +	if (!vm) {
> > +		pr_err("%s: could not get videomode %d\n", __func__, index);
> > +		return -EINVAL;
> > +	}
> 
> This can't happen. If vm is NULL the videomode_from_timing call above will 
> return -EINVAL, and this function will then return immediately without 
> reaching this code block.
> 

Okay.

> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(of_get_videomode);
> > +
> > +#if defined(CONFIG_DRM)
> > +int videomode_to_display_mode(struct videomode *vm, struct drm_display_mode
> > *dmode)
> > +{
> > +	memset(dmode, 0, sizeof(*dmode));
> > +
> > +	dmode->hdisplay = vm->hactive;
> > +	dmode->hsync_start = dmode->hdisplay + vm->hfront_porch;
> > +	dmode->hsync_end = dmode->hsync_start + vm->hsync_len;
> > +	dmode->htotal = dmode->hsync_end + vm->hback_porch;
> > +
> > +	dmode->vdisplay = vm->vactive;
> > +	dmode->vsync_start = dmode->vdisplay + vm->vfront_porch;
> > +	dmode->vsync_end = dmode->vsync_start + vm->vsync_len;
> > +	dmode->vtotal = dmode->vsync_end + vm->vback_porch;
> > +
> > +	dmode->clock = vm->pixelclock / 1000;
> > +
> > +	if (vm->hah)
> > +		dmode->flags |= DRM_MODE_FLAG_PHSYNC;
> > +	else
> > +		dmode->flags |= DRM_MODE_FLAG_NHSYNC;
> > +	if (vm->vah)
> > +		dmode->flags |= DRM_MODE_FLAG_PVSYNC;
> > +	else
> > +		dmode->flags |= DRM_MODE_FLAG_NVSYNC;
> > +	if (vm->interlaced)
> > +		dmode->flags |= DRM_MODE_FLAG_INTERLACE;
> > +	if (vm->doublescan)
> > +		dmode->flags |= DRM_MODE_FLAG_DBLSCAN;
> > +	drm_mode_set_name(dmode);
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(videomode_to_display_mode);
> > +
> > +int of_get_drm_display_mode(struct device_node *np, struct drm_display_mode
> > *dmode,
> > +			int index)
> 
> Same as above, do we really need to expose this helper function ? If so we 
> should at least clearly document (using kerneldoc for instance) that drivers 
> should only use it if they need to get a single mode once.
> 
> > +{
> > +	struct videomode vm;
> > +	int ret;
> > +
> > +	ret = of_get_videomode(np, &vm, index);
> > +
> > +	if (ret)
> > +		return ret;
> > +
> > +	videomode_to_display_mode(&vm, dmode);
> > +
> > +	pr_info("%s: got %dx%d display mode from %s\n", __func__, vm.hactive,
> > +		vm.vactive, np->name);
> > +	dump_drm_displaymode(dmode);
> > +
> > +	return 0;
> > +
> > +}
> > +EXPORT_SYMBOL_GPL(of_get_drm_display_mode);
> > +#else
> > +int videomode_to_display_mode(struct videomode *vm, struct drm_display_mode
> > *dmode)
> > +{
> > +	return 0;
> > +}
> > +
> > +int of_get_drm_display_mode(struct device_node *np, struct drm_display_mode
> > *dmode,
> > +			int index)
> > +{
> > +	return 0;
> > +}
> 
> What about not defining those if CONFIG_DRM is not set ? No driver should call 
> these functions in that case. If we really need those stubs they should return 
> an error.
> 

Okay. I will remove them.

> > +#endif
> > +
> > +int videomode_to_fb_videomode(struct videomode *vm, struct fb_videomode
> > *fbmode)
> > +{
> > +	memset(fbmode, 0, sizeof(*fbmode));
> > +
> > +	fbmode->xres = vm->hactive;
> > +	fbmode->left_margin = vm->hback_porch;
> > +	fbmode->right_margin = vm->hfront_porch;
> > +	fbmode->hsync_len = vm->hsync_len;
> > +
> > +	fbmode->yres = vm->vactive;
> > +	fbmode->upper_margin = vm->vback_porch;
> > +	fbmode->lower_margin = vm->vfront_porch;
> > +	fbmode->vsync_len = vm->vsync_len;
> > +
> > +	fbmode->pixclock = KHZ2PICOS(vm->pixelclock) / 1000;
> > +
> > +	if (vm->hah)
> > +		fbmode->sync |= FB_SYNC_HOR_HIGH_ACT;
> > +	if (vm->vah)
> > +		fbmode->sync |= FB_SYNC_VERT_HIGH_ACT;
> > +	if (vm->interlaced)
> > +		fbmode->vmode |= FB_VMODE_INTERLACED;
> > +	if (vm->doublescan)
> > +		fbmode->vmode |= FB_VMODE_DOUBLE;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(videomode_to_fb_videomode);
> > +
> > +int of_get_fb_videomode(struct device_node *np, struct fb_videomode *fb,
> > +			int index)
> > +{
> > +	struct videomode vm;
> > +	int ret;
> > +
> > +	ret = of_get_videomode(np, &vm, index);
> > +	if (ret)
> > +		return ret;
> > +
> > +	videomode_to_fb_videomode(&vm, fb);
> > +
> > +	pr_info("%s: got %dx%d display mode from %s\n", __func__, vm.hactive,
> > +		vm.vactive, np->name);
> > +	dump_fb_videomode(fb);
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(of_get_drm_display_mode);
> > diff --git a/include/linux/of_videomode.h b/include/linux/of_videomode.h
> > new file mode 100644
> > index 0000000..96efe01
> > --- /dev/null
> > +++ b/include/linux/of_videomode.h
> > @@ -0,0 +1,41 @@
> > +/*
> > + * Copyright 2012 Steffen Trumtrar <s.trumtrar@pengutronix.de>
> > + *
> > + * generic videomode description
> > + *
> > + * This file is released under the GPLv2
> > + */
> > +
> > +#ifndef __LINUX_VIDEOMODE_H
> > +#define __LINUX_VIDEOMODE_H
> > +
> > +#include <drm/drmP.h>
> > +
> > +struct videomode {
> > +	u32 pixelclock;
> > +	u32 refreshrate;
> > +
> > +	u32 hactive;
> > +	u32 hfront_porch;
> > +	u32 hback_porch;
> > +	u32 hsync_len;
> > +
> > +	u32 vactive;
> > +	u32 vfront_porch;
> > +	u32 vback_porch;
> > +	u32 vsync_len;
> > +
> > +	bool hah;
> > +	bool vah;
> > +	bool interlaced;
> > +	bool doublescan;
> > +
> > +};
> > +
> > +int videomode_to_display_mode(struct videomode *vm, struct drm_display_mode
> > *dmode); +int videomode_to_fb_videomode(struct videomode *vm, struct
> > fb_videomode *fbmode); +int of_get_videomode(struct device_node *np, struct
> > videomode *vm, int index); +int of_get_drm_display_mode(struct device_node
> > *np, struct drm_display_mode *dmode, +			int index);
> > +int of_get_fb_videomode(struct device_node *np, struct fb_videomode *fb,
> > int index); +#endif /* __LINUX_VIDEOMODE_H */
> -- 
> Regards,
> 
> Laurent Pinchart
> 

Regards,

Steffen
-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |